A variety of apparatus have been proposed to keep a driver alert and prevent a driver of automobiles and the like, from dozing during driving. Such apparatus usually comprise a sensor for sensing that a driver has started to doze and means for wakening a driver by receiving a signal from the sensor. For example, there is a sensor which senses that a driver has started to doze by sensing the number of times the driver nods per unit time or the time for leaning one's head forward, and the like, because a driver nods when the driver starts to doze, and sends a signal to means for alerting the driver. Also, there are means for alerting a driver which operates by receiving the signal, and alerting the driver by producing a loud sound in the driver's ear or ears. Therefore, according to this apparatus, if a driver starts to doze, the sensor senses that the driver's head is leaning forward, and actuates the means for alerting or wakening the driver.